The long range objectives of this proposal are to develop non-invasive MRI and MRS methods for the early evaluation of the response of breast cancer to hormonal therapy and to help improve endocrine therapy of breast cancer. The proposed experiments were designed to test out hypothesis that the expressions of the isoforms of vascular endothelial growth factor (VEGF) are hormonally regulated and this, in turn, modifies tumor vascularity and perfusion in a specific manner which determines the results of therapy. The integration of molecular Biology and MRI studies will involve studies in human breast cancer cells and tumors in nude mice under varying hormonal manipulations with estrogen, tamoxifen and the new derivative of tamoxifen-tamoxifen methiodide (TMI). The specific aims are designed to test the above hypothesis and to characterize at the molecular, cellular and whole tumor levels the effects of anti-estrogens, particularly tamoxifen and TMI, on the various VEGF isoforms and on the density, permeability and perfusion capacity of breast cancer vasculature. These aims include the use of molecular biology methods that will be used to establish the mRNA levels and protein levels of VEGF isoforms in vitro and to map the expression of VEGF in vivo, under varying hormonal treatments. In addition, they plan to continue the development and application of MRI and MRS methods to monitor in vivo the hormonal induced changes in the vasculature and other pathophysiologic characteristics. Finally, this proposal is also designed to test the pharmacokinetics, potency and mechanism of activity of TMI. This work will add to the basic understanding of breast cancer angiogenesis and may also help design and improve new anti-estrogen and anti-angiogenic therapy of breast cancer. The results of the MRI studies in animal models will serve as a basis for developing clinical protocols for non-invasive and early monitoring of response to hormonal therapy.